Chimeric antigen receptor T cells (CAR T cells) are dosed similarly to donor lymphocyte infusions following hematopoietic cell transplantation. However, the mechanism driving proliferation in CAR T cells is distinct from conventional T cells. As such there are quantitative differences in the antigen response of these engineered cells when compared with conventional T cells. In this perspective paper the logistic equation of growth is used to develop a mathematical basis for understanding the difference between CAR T cell and conventional T cell response to antigen burden.